The invention relates to an apparatus for forming and deep-drawing the neck region at the edge of a plastics half shell, having a deep-drawing tool and a counter-pressure plate which are movable in two directions relative to each other, wherein the deep-drawing tool embraces a deep-drawing cavity in shell-like manner and has a recess in the side wall at the edge.
DE-PS 40 05 972 discloses an apparatus similar to the afore-mentioned kind for deep-drawing a shell made of plastics material which is open on one side. This apparatus can be used, for example, to deep-draw two half shells which are subsequently welded and joined together by virtue of their residual heat in such a way that a hollow pack for liquids is produced. With this known apparatus. for purposes of filling, closing and pouring, a neck region was formed at the edge of each plastics half shell with a semi-cylindrical casing-like collar in such a way that after the two half shells were joined together a top was produced with a hole, at the outer edge of which a cylindrical casing-like collar projected from the top of the pack.
In order to create a recess in the neck region at the edge of the plastics half shell, for the purpose of forming this collar, the heated counter-pressure plate has been provided with a partially frustoconical projection, which, when compressed against a counter-pressure plate can be driven into a recess in same, wherein the plastics plate which is placed between the counter-pressure plate and the counter-heating plate is subject to deformation at one place on the edge where the neck region is to be produced on the plastics half shell. This was, and still is, necessary for the edge of the plastics plate to be able to be placed and pressed sealingly into the recess of the deep-drawing tool before it is deep-drawn to form the half shell. With the known apparatus, this happened by way of the projection of the counter-pressure plate which was able to be heated and to move backwards and forwards vertically. It was able to move both horizontally relative to the deep-drawing tool and also relative to the counter-heating plate, and was also able to move relative to the deep-drawing tool vertically from one operating position to the next, in order to make it possible for the workpiece, the flat plastics plate, to move from the heating position into the deep-drawing position and then to enable it to be deep-drawn in the form of the half shell.
For deep-drawing, the plastics plate has to be heated to a suitably high temperature, and this is done in the known case between various counter-pressure plates and counter-heating plates which had the drawback that in the region of the recess of the counter-heating plate the plastics plate was not heated sufficiently, at the very place where deformation of the neck region had to take place. Therefore, attempts were made to overheat the plastics plate before the neck region was formed out or rough formed, so that the forming out process or the stretching process was possible at all. However, this was disadvantageous in that non-uniform stretches in the material occurred. In addition, there has been the problem that due to the two-stage treatment of the plastics plate, namely the rough forming of the neck region in the heating position and subsequent deep-drawing in a deep-drawing position at a distance therefrom, the counter-pressure plate basically only holds the plastics plate by way of suction. During rough forming in the neck region at the edge of the plastics plate, the suction force was often insufficient, with the result that the plastics sheet migrated regionally. This undesirable migration led to deformation in the neck region, and, in particular, at the desired collar on the hole of the subsequent pack. The deformed collars resulting now and then with the ready pack also resulted in regions of unsealing.